This application claims priority to Korean Patent Application No. 10-2004-0006949, filed on Feb. 3, 2004, which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a field emission type backlight device. More particularly, it relates to a field emission type backlight device capable that may have improved luminance uniformity and reduced power consumption.
2. Description of the Related Art
Liquid crystal displays (LCDs) often require a backlight device. A cold cathode fluorescent lamp (CCFL) has been commonly used as a line light source, and a light emitting diode (LED) as a point light source. More recently, field emission devices are being explored as alternative light sources. A field emission type backlight device has low power consumption and a relatively uniform luminance even in a wide area of light emission.
FIG. 1A is a sectional view showing a conventional field emission type backlight device. FIG. 1B is a plan view showing a cathode electrode on a lower substrate.
Upper and lower substrates 20 and 10 face each other, separated by a gap. An anode electrode 22 and a fluorescent layer 24 are sequentially provided on a lower side of the upper substrate 20. On an upper side of the lower substrate 10 a cathode electrode 12 is provided as an electron emission source. In a field emission type backlight device having such a structure, electrons are emitted from the cathode electrode 12 when a voltage is applied between the anode electrode 22 and the cathode electrode 12. When the electrons collide against the fluorescent layer 24, it radiates visible light.
In such a backlight device, an example of which is shown in FIG. 1B, the cathode electrode 12 is provided on the entire surface of the lower substrate 10. In such a structure, luminance uniformity tends to decrease if the cathode electrode 12 is not uniform in thickness. Also, non-uniform emission tends to occur due to concentration of electric field in the edge of the cathode electrode 12.
FIGS. 2A and 2B depict a field emission device designed to solve the problems with the device shown in FIGS. 1A and 1B. FIG. 2A is a sectional view showing a field emission type backlight device. FIG. 2B is a plan view showing a cathode electrode and a gate electrode on a lower substrate.
Upper and lower substrates 40 and 30 are disposed to face each other with a predetermined gap therebetween. An anode electrode 42 and a fluorescent layer 44 are sequentially provided on a lower side of the upper substrate 40. Line-shaped cathode electrodes 32 and gate electrodes 33 are alternatively provided on an upper side of the lower substrate 30.
In such a device, since cathode electrodes 32 are connected to each other in series and gate electrodes 33 are connected to each other in series, resistance between beginning and end portions of the signal voltage line connecting the electrodes may be large. In addition, the bigger the display, the larger the resistance between beginning and end portions of the signal voltage line. This can lead to differences in input voltage and delay in signal pulse. This may cause luminance difference between beginning and end portions of the signal voltage line.
Moreover, capacitance varies depending on the gap between the cathode and gate electrodes 32 and 33, and capacitance increases greatly as the gap between the cathode and gate electrodes 32 and 33 narrows. The gap may be narrowed to improve current characteristic by dropping the operating voltage. Power consumption increases as line resistance and capacitance grow larger.